Description

This track shows regions of the genome that are alignable to other genomes ("chain" subtracks) or in synteny ("net" subtracks). The alignable parts are shown with thick blocks that look like exons. Non-alignable parts between these are shown like introns.

Chain Track

The chain track shows alignments of mouse (Jun. 2020 (GRCm39/mm39)) to the pika genome using a gap scoring system that allows longer gaps than traditional affine gap scoring systems. It can also tolerate gaps in both mouse and pika simultaneously. These "double-sided" gaps can be caused by local inversions and overlapping deletions in both species.

The chain track displays boxes joined together by either single or double lines. The boxes represent aligning regions. Single lines indicate gaps that are largely due to a deletion in the mouse assembly or an insertion in the pika assembly. Double lines represent more complex gaps that involve substantial sequence in both species. This may result from inversions, overlapping deletions, an abundance of local mutation, or an unsequenced gap in one species. In cases where multiple chains align over a particular region of the pika genome, the chains with single-lined gaps are often due to processed pseudogenes, while chains with double-lined gaps are more often due to paralogs and unprocessed pseudogenes.

In the "pack" and "full" display modes, the individual feature names indicate the chromosome, strand, and location (in thousands) of the match for each matching alignment.

Net Track

The net track shows the best mouse/pika chain for every part of the pika genome. It is useful for finding syntenic regions, possibly orthologs, and for studying genome rearrangement. The mouse sequence used in this annotation is from the Jun. 2020 (GRCm39/mm39) assembly.

Display Conventions and Configuration

Chain Track

By default, the chains to chromosome-based assemblies are colored based on which chromosome they map to in the aligning organism. To turn off the coloring, check the "off" button next to: Color track based on chromosome.

To display only the chains of one chromosome in the aligning organism, enter the name of that chromosome (e.g. chr4) in box next to: Filter by chromosome.

Net Track

In full display mode, the top-level (level 1) chains are the largest, highest-scoring chains that span this region. In many cases gaps exist in the top-level chain. When possible, these are filled in by other chains that are displayed at level 2. The gaps in level 2 chains may be filled by level 3 chains and so forth.

In the graphical display, the boxes represent ungapped alignments; the lines represent gaps. Click on a box to view detailed information about the chain as a whole; click on a line to display information about the gap. The detailed information is useful in determining the cause of the gap or, for lower level chains, the genomic rearrangement.

Individual items in the display are categorized as one of four types (other than gap):

• Top - the best, longest match. Displayed on level 1.
• Syn - line-ups on the same chromosome as the gap in the level above it.
• Inv - a line-up on the same chromosome as the gap above it, but in the opposite orientation.
• NonSyn - a match to a chromosome different from the gap in the level above.

Methods

Chain track

Transposons that have been inserted since the mouse/pika split were removed from the assemblies. The abbreviated genomes were aligned with lastz, and the transposons were added back in. The resulting alignments were converted into axt format using the lavToAxt program. The axt alignments were fed into axtChain, which organizes all alignments between a single mouse chromosome and a single pika chromosome into a group and creates a kd-tree out of the gapless subsections (blocks) of the alignments. A dynamic program was then run over the kd-trees to find the maximally scoring chains of these blocks. The following matrix was used:

	A	C	G	T
A	91	-114	-31	-123
C	-114	100	-125	-31
G	-31	-125	100	-114
T	-123	-31	-114	91

-linearGap=medium

tableSize    11
smallSize   111
position  1   2   3   11  111  2111  12111  32111   72111  152111  252111
qGap    350 425 450  600  900  2900  22900  57900  117900  217900  317900
tGap    350 425 450  600  900  2900  22900  57900  117900  217900  317900
bothGap 750 825 850 1000 1300  3300  23300  58300  118300  218300  318300

Net track

Chains were derived from lastz alignments, using the methods described on the chain tracks description pages, and sorted with the highest-scoring chains in the genome ranked first. The program chainNet was then used to place the chains one at a time, trimming them as necessary to fit into sections not already covered by a higher-scoring chain. During this process, a natural hierarchy emerged in which a chain that filled a gap in a higher-scoring chain was placed underneath that chain. The program netSyntenic was used to fill in information about the relationship between higher- and lower-level chains, such as whether a lower-level chain was syntenic or inverted relative to the higher-level chain. The program netClass was then used to fill in how much of the gaps and chains contained Ns (sequencing gaps) in one or both species and how much was filled with transposons inserted before and after the two organisms diverged.

Credits

Lastz (previously known as blastz) was developed at Pennsylvania State University by Minmei Hou, Scott Schwartz, Zheng Zhang, and Webb Miller with advice from Ross Hardison.

Lineage-specific repeats were identified by Arian Smit and his RepeatMasker program.

The axtChain program was developed at the University of California at Santa Cruz by Jim Kent with advice from Webb Miller and David Haussler.

The browser display and database storage of the chains and nets were created by Robert Baertsch and Jim Kent.

The chainNet, netSyntenic, and netClass programs were developed at the University of California Santa Cruz by Jim Kent.

References

Harris, R.S. (2007) Improved pairwise alignment of genomic DNA Ph.D. Thesis, The Pennsylvania State University

Chiaromonte F, Yap VB, Miller W. Scoring pairwise genomic sequence alignments. Pac Symp Biocomput. 2002:115-26. PMID: 11928468

Kent WJ, Baertsch R, Hinrichs A, Miller W, Haussler D. Evolution's cauldron: duplication, deletion, and rearrangement in the mouse and human genomes. Proc Natl Acad Sci U S A. 2003 Sep 30;100(20):11484-9. PMID: 14500911; PMC: PMC208784

Schwartz S, Kent WJ, Smit A, Zhang Z, Baertsch R, Hardison RC, Haussler D, Miller W. Human-mouse alignments with BLASTZ. Genome Res. 2003 Jan;13(1):103-7. PMID: 12529312; PMC: PMC430961